Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.

For more information on the Visual Elements image see the Uses and properties section below.



A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.

Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).

Atomic number
The number of protons in an atom.

Electron configuration
The arrangements of electrons above the last (closed shell) noble gas.

Melting point
The temperature at which the solid–liquid phase change occurs.

Boiling point
The temperature at which the liquid–gas phase change occurs.

The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.

Density (g cm−3)
Density is the mass of a substance that would fill 1 cm3 at room temperature.

Relative atomic mass
The mass of an atom relative to that of carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists, the value given is the abundance weighted average.

Atoms of the same element with different numbers of neutrons.

CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems.

Fact box

Group 16  Melting point 449.51°C, 841.12°F, 722.66 K 
Period Boiling point 988°C, 1810°F, 1261 K 
Block Density (g cm−3) 6.232 
Atomic number 52  Relative atomic mass 127.60  
State at 20°C Solid  Key isotopes 130Te 
Electron configuration [Kr] 4d105s25p4  CAS number 13494-80-9 
ChemSpider ID 4885717 ChemSpider is a free chemical structure database


Image explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


The description of the element in its natural form.

Biological role

The role of the element in humans, animals and plants.

Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

Uses and properties

Image explanation
The Earth-like sphere in the image reflects the origin of the element’s name, after ‘tellus’, the Latin word for Earth.
A semi-metal usually obtained as a grey powder.
Tellurium is used in alloys, mostly with copper and stainless steel, to improve their machinability. When added to lead it makes it more resistant to acids and improves its strength and hardness.

Tellurium has been used to vulcanise rubber, to tint glass and ceramics, in solar cells, in rewritable CDs and DVDs and as a catalyst in oil refining. It can be doped with silver, gold, copper or tin in semiconductor applications.
Biological role
Tellurium has no known biological role. It is very toxic and teratogenic (disturbs the development of an embryo or foetus). Workers exposed to very small quantities of tellurium in the air develop ‘tellurium breath’, which has a garlic-like odour.
Natural abundance
Tellurium is present in the Earth’s crust only in about 0.001 parts per million. Tellurium minerals include calaverite, sylvanite and tellurite. It is also found uncombined in nature, but only very rarely. It is obtained commercially from the anode muds produced during the electrolytic refining of copper. These contain up to about 8% tellurium.
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Tellurium was discovered in 1783 by Franz Joseph Müller von Reichenstein at Sibiu, Romania. He became intrigued by ore from a mine near Zalatna which had a metallic sheen and which he suspected was native antimony or bismuth. (It was actually gold telluride, AuTe2.) Preliminary investigation showed neither antimony nor bismuth to be present. For three years Müller researched the ore and proved it contained a new element. He published his findings in an obscure journal and it went largely unnoticed.

In 1796, he sent a sample to Martin Klaproth in Berlin who confirmed him findings. Klaproth produced a pure sample and decided to call it tellurium. Rather strangely, this was not the first sample of tellurium to pass through his hands. In 1789, he had been sent some by a Hungarian scientist, Paul Kitaibel who had independently discovered it.

Atomic radius, non-bonded
Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.

Covalent radius
Half of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.

Electron affinity
The energy released when an electron is added to the neutral atom and a negative ion is formed.

Electronegativity (Pauling scale)
The tendency of an atom to attract electrons towards itself, expressed on a relative scale.

First ionisation energy
The minimum energy required to remove an electron from a neutral atom in its ground state.

Atomic data

Atomic radius, non-bonded (Å) 2.06 Covalent radius (Å) 1.37
Electron affinity (kJ mol−1) 190.161 Electronegativity
(Pauling scale)
Ionisation energies
(kJ mol−1)


Common oxidation states

The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.


Atoms of the same element with different numbers of neutrons.

Key for isotopes

Half life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Oxidation states and isotopes

Common oxidation states 6, 4, -2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  120Te 119.904 0.09 1.9 x 1017 β+EC 
  122Te 121.903 2.55
  123Te 122.904 0.89 > 9.2 x 1016 EC 
  124Te 123.903 4.74
  125Te 124.904 7.07
  126Te 125.903 18.84
  128Te 127.904 31.74 2.2 x 1024 β-β- 
  130Te 129.906 34.08 8 x 1020 β-β- 


Data for this section been provided by the British Geological Survey.

Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.

Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.

Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.


The availability of suitable substitutes for a given commodity.
High = substitution not possible or very difficult.
Medium = substitution is possible but there may be an economic and/or performance impact
Low = substitution is possible with little or no economic and/or performance impact

Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.

Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.

Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.

Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.

Supply risk

Relative supply risk Unknown
Crustal abundance (ppm) 0.001
Recycling rate (%) Unknown
Substitutability Unknown
Production concentration (%) Unknown
Reserve distribution (%) Unknown
Top 3 producers
  • Unknown
Top 3 reserve holders
  • Unknown
Political stability of top producer Unknown
Political stability of top reserve holder Unknown


Specific heat capacity (J kg−1 K−1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.

Young's modulus

A measure of the stiffness of a substance. It provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.

Shear modulus

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.

Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour pressure

A measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

Specific heat capacity
(J kg−1 K−1)
202 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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Listen to Tellurium Podcast
Transcript :

Chemistry in its element: tellurium


You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

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Chris Smith

Hello! This week Dr. Who gets to mention, as we unlock the story of a slimy element, that makes people stink of garlic and turns their fingers black. With the tale of tellurium, here's Peter Wothers.

Peter Wothers

Tellurium, it sounds like a Dr. Who monster and in a number of ways this element does have a few properties that would make it suitable for any good outer space, sci-fi horror movie. For a start, like many space monsters, it comes from slime; to be precise it is extracted from anode slime, a waste product formed during the electrolytic refining of copper. Its special power, well in the form of cadmium telluride, it can capture solar energy. Far from being used for evil though, this compound has been used in some of the most efficient solar cells for the generation of electrical power.

Every good monster must have a secret weapon and tellurium is no exception. It gives its enemies garlic breath, really bad garlic breath. A dose of half a microgram, hardly even visible would give you garlic breath for 30 hours, Oh! And it also gives its victim black patches on the webbing in between the fingers, but few people would get close enough to notice this. Like a certain well-known vampire, tellurium was first discovered in Transylvania. This was in 1783 by Franz Joseph Muller von Reichenstein, the chief inspector of the mines there. He was having particular problems with the analysis of an unusual gold containing ore. Eventually, he managed to isolate a new metal from the ore and he called it aurum problematicum. He sent a sample to the German chemist Martin Klaproth, who confirmed it was a new element and gave it the name tellurium. But to properly understand why he called it this, we need to go way back in time and look into space.

When early man looked up at the stars at night, he noticed certain heavenly bodies that moved through the fixed pattern of the stars. These were the planets Mercury, Venus, Mars, Jupiter and Saturn. Two other great bodies also seemed to circle the earth, namely the Sun and the Moon. Altogether then there were seven such heavenly bodies and seven was a magical number. Early man also knew of just seven metals, gold, silver, copper, iron, tin, lead and mercury; surely this could be no coincidence. In the same ways that rays from the sun nourish plants and are essential for their growth, it was thought that the invisible rays from the planets helped nourish metallic ores in the ground. Each planet was thought to have a particular influence on one metal or its ores. Chaucer described this connection in the 14th Century. The Sun is associated with gold, the Moon with silver, Mars with iron, Saturn with lead, Jupiter with tin and Venus with copper and even today, we still keep the same name for both the planet and the element, Mercury. The association between gold and the Sun seems fairly obvious from their colours, similarly the connection between silver and the Moon. The other connections are little more vague. A 17th Century text quotes, "Iron is called by the name of Mars whether employed for the making of weapons of war, of which Mars was said to be the God or because of the influences from which iron receives from this planet." It is interesting that we now know that the colour of this red planet is due to the oxides of iron. The chemists called copper, Venus both by reason of the influences, which possibly it receives from that planet and of the virtue it had in diseases seated in the purpose of generation. This is referring to early treatments of venereal diseases, the diseases of Venus. Being the planet closest to the Sun, Mercury moves through space faster than any other. It takes Mercury just 88 days to orbit the Sun, compared to our 365 days. Perhaps, this speedy motion was one of the reasons for the lasting association between the metal and the planet or perhaps it is as described in one book "due to the fact that the element has an aptness to change its figure, a property attributed by the heathens to mercury, one of their false Gods." The connection between the elements tin and lead with Jupiter and Saturn were even more dubious.

Unfortunately, the magic number of 7 metals didn't last. For a while, early chemists, just conveniently passed over antimony, arsenic, bismuth, zinc and cobalt. After all they weren't real metals, but with the discovery of platinum, they could ignore it no more. For a while, platinum was even known as the eighth metal. Still more metals were discovered, but then in 1781, a new planet was discovered, Uranus. Just as the ancient God, Saturn or Cronus was the father of Jupiter or Zeus, the new planet should be named after the father of Saturn, hence Uranus, after the Greek God of the sky. In recognition of this discovery in 1789, Klaproth named a new metal he had discovered after this element, uranium. So in 1798, when Klaproth had the chance to name another element, he named it after the only then known planet in the Solar System that did not have an element named after it, the Earth. In ancient mythology, Tellus or Terra or Gaea was the goddess of the Earth and the wife of Uranus, the God of the Skies. Thus was born tellurium.

Chris Smith

A chemist, who takes his inspiration from the heavens, that was Peter Wothers from Cambridge University, telling the story of tellurium. Next time, the illuminating tale of a gas that everyone thought wasn't worth the time of day.

Victoria Gill

And initially its lack of reactivity meant there were no obvious uses for Neon. It took a bit of imagination from the French engineer, chemist and inventor, Georges Claude, who early in the 20th Century first applied an electric discharge to a sealed tube of neon gas. The red glow it produced, gave Claude the idea of manufacturing a source of light in an entirely new way. He made glass tubes which could be used just like light bulbs. Claude displayed the first neon lamp to the public on December 11, 1910 at an exhibition in Paris. His striking display turned heads but unfortunately sold no Neon tubes. People simply didn't want to illuminate their homes with red light.

Chris Smith
But they did want to see their names written in lights and that's exactly what Georges Claude did next as Victoria Gill will be telling us next time. I hope you can join us. I'm Chris Smith, thank you for listening. And Goodbye!


Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by There's more information and other episodes of Chemistry in its element on our website at

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Visual Elements images and videos
© Murray Robertson 1998-2017.



W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.


Uses and properties

John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.


Supply risk data

Derived in part from material provided by the British Geological Survey © NERC.


History text

Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.



Produced by The Naked Scientists.


Periodic Table of Videos

Created by video journalist Brady Haran working with chemists at The University of Nottingham.